Context: Binge-eating disorder (BED) - a syndrome that only recently has attracted scientific attention - is often seen in obese individuals, especially those with severe obesity. However, it remains unclear whether BED represents an etiologically distinct behavioral phenotype of obesity or simply a nonspecific eating pattern sometimes seen in obese individuals. Objective: To test whether BED aggregates in families independently of obesity, and if so, whether familial factors for BED also independently increase the risk of obesity. Design, Patients, and Setting: Blinded family interview study of overweight or obese probands with (n=150) and without (n=150) BED, and their first-degree relatives (n=888) in a community setting evaluated between October 2002 and July 2004. Main Outcome Measures: Lifetime diagnosis of BED; current and highest lifetime body mass index (calculated as the weight in kilograms divided by the square of the height in meters). Results: Binge-eating disorder aggregated strongly in families independently of obesity (odds ratio, 2.2; 95% confidence interval, 1.4-3.6; P<.001). Furthermore, relatives of probands with BED displayed a markedly higher prevalence of severe obesity in adulthood (body mass index ≥40) than relatives of probands without BED even when controlling for proband body mass index (odds ratio, 2.5; 95% confidence interval, 1.4-4.4; P=.002). Conclusions: Binge-eating disorder is a familial disorder caused in part by factors distinct from other familial factors for obesity. Furthermore, these BED-specific familial factors may independently increase the risk of obesity, especially severe obesity. It follows that targeted interventions capable of preventing or treating traits influenced by these BED-specific familial factors could reduce the public health burden of obesity.